1. Field of the Invention
The present invention relates to a plate processing machine such as drilling machines punch presses etc. for processing a plate workpiece, and more specifically to a plate processing machine provided with a device for moving and positioning a plate workpiece in both the X- and Y-axis directions relative to a process position at which a tool set and wherein a die and a punch is arranged.
2. Description of the Prior Art
Drilling machines or punch presses are well known, such as a plate processing machine for automatically processing a plate workpiece in accordance with appropriate machining processes. In general, these machines are provided with a workpiece moving and positioning device for moving a workpiece in the X-axis direction (the lateral direction of the machine) and the Y-axis direction (the longitudinal direction of the machine) and positioning the workpiece at an appropriate process position.
In the conventional workpiece moving and positioning device, a carriage base reciprocably movable in the Y-axis direction is usually provided, and further a carriage having a pair of work clamping devices for holding a workpiece is mounted on the carrier base so as to be reciprocably movable is the X-axis direction. In more detail, the carriage base is arranged extending in the X-axis direction in such a way that both the ends thereof are movably supported by guide members disposed on both the ends of a machine base and extending in the Y-axis direction. The carriage is reciprocably supported by guide members provided on the base and extending in the Y-axis direction. Further, a drive unit for moving the carriage is usually mounted on one end of the carriage base due to a consideration of the convenience in assembling or maintenance work.
In the above-mentioned conventional workpiece moving and positioning apparatus, the carriage base is moved and positioned automatically in the Y-axis direction and the carriage is moved and positioned automatically in the X-axis direction in order to move a workpiece to a predetermined process position, both under the control of an NC system.
In the conventional device, however, when the above-mentioned workpiece moving and positioning operation is effected and therefore the carriage is moved toward one side of the base where the drive unit is mounted, an addition of a carriage weight and a drive unit weight is applied to one side of the base, so that the carriage base becomes inclined from the horizontal plane of the machine. In addition, a friction generated between the guide member and the carriage base on one side of the base where the drive unit is mounted increases greatly as compared with a friction generated between the two on the other side of the base remote from the drive unit; as a result, when the carriage base is moved in the Y-axis direction, there exists a tendency that one side of the carriage base loaded with the carriage weight and the drive unit weight is moved being delayed from the other side thereof, thus resulting in a problem such that the carriage base is somewhat inclined from the horizontal plane and from the X-axis and thus the precision in workpiece positioning operation is deteriorated on the order of several hundred millimeters, for instance, relative to a true machining position of the plate processing machine.
Further, in the plate processing machine, a workpiece is generally supported by such a construction that a pair of movable tables are provided integral with the carriage of the workpiece moving and positioning device and a fixed table is disposed between the two movable tables. In more detail, a workpiece is movably supported by a great number of free ball bearings rotatably arranged on the two movable tables and the fixed table.
Therefore, since a workpiece is supported by the free ball bearings in point contact manner, when the workpiece is moved at a high speed, the rotation of the free ball bearings cannot follow up the moving workpiece and therefore a relative sliding motion is produced between the workpiece and the free ball bearings, thus resulting in the other problem such that scratches are readily produced on the under surface of the workpiece.
To overcome the above problem, a structure has been developed such that a caterpillar table is arranged between the two movable tables so as to be movable together with the carriage base. In this arrangement, since the tables and the carriage base are moved together in the Y-axis direction when the carriage base is moved in the Y-axis direction to move a workpiece in the same direction, no relative sliding motion is advantageously produced between the workpiece and the tables. However, there still exist other problems as described below: For instance, in the case of a turret punch press, it is necessary to determine the dimension of the caterpillar table width a little greater than a diameter of the relatively large turret, in spite of a small process area where a punch and a die are arranged. That is, the width of the caterpillar table is extremely great in comparison with the processing area. Therefore, when the workpiece is being moved, a workpiece is brought into contact with the upper surface of a number of dies arranged on the turret under the same condition as in the conventional machine, thus scratches are readily produced on the workpiece.
In addition, if the caterpillar table vibrates during motion, scratches are further produced on the under surface of the workpiece, and additionally the workpiece positioning time is inevitably increased.
Furthermore, in the conventional plate processing machine, there exists a drawback in that since a processed workpiece is carried out toward movable tables, the space required for laying out a plate processing line is enlarged.